This invention relates to an electric actuator provided with a brake and adapted for use with mechanisms such as automatic drive mechanisms for controlling a travelling speed of vehicle at a preset value.
Generally, an automatic drive mechanism serves to automatically drive a throttle link connected to a throttle valve of a vehicle by means of an electric motor, thereby to automatically control the vehicle speed in accordance with instructions from a controller.
An electric actuator for this type of automatic drive mechanism comprises an electric motor, reduction gears for reducing the rotational speed of the electric motor, and a brake for selectively transmitting the output of the reduction gears to the throttle valve of the vehicle to be controlled. As a brake, an electromagnetic brake readily controllable by an electrical output are conventionally used. Such electromagnetic brake includes a coil bobbin enclosed by an electromagnetic yoke formed in two pieces, and an electromagnetic coil wound around the coil bobbin. Since the electromagnetic coil is rotated by the reduction gears, it has hitherto been necessary to energize the electromagnetic coil through slip-ring type contacts.
Such type of automatic drive mechanism has disadvantages such that the slip-ring type contacts may give rise to a contact failure and also that the construction of the automatic drive mechanism becomes complicated.